What is the best alternative to Thirteen Explore on iPhone?

CuriosityStream, S tier, #1 in documentary streaming.

Is there a free alternative to Thirteen Explore?

Yes: CuriosityStream (S tier, #1) is free to download, with in-app purchases.

Yes. 7 apps rank above it in documentary streaming: CuriosityStream (#1), MagellanTV Documentaries (#2), Kanopy (#3) and more.

Thirteen Explore is D tier, #8 of 8 in documentary streaming. Here is everything that competes with it on iPhone, in tier order.

1
CuriosityStreamShigher tier
Free + IAP · ★ 4.6 · 6,269 ratings · score 92
Documentary and non-fiction streaming app covering science, nature, history, and biographies, with downloadable shows.
2
MagellanTV DocumentariesShigher tier
Free download · ★ 4.6 · 3,879 ratings · score 92
Documentary streaming app with genre collections in History, Nature, Science, Space and Crime, offered as a membership.
3
KanopyShigher tier
Free · ★ 4.8 · 152,417 ratings · score 91
Streams films and documentaries free of ads through a public library card sign-up.
4
PBS: Watch TV & DocumentariesShigher tier
Free download · ★ 4.9 · 356,455 ratings · score 89
Free app for streaming PBS TV series, films, documentaries, and news, including live local PBS station TV.
5
TrueShort - Stream True CrimeShigher tier
Free + IAP · ★ 4.9 · 18,304 ratings · score 89
Short-form true crime documentary series of 60-second episodes, presented as vertical video for mobile phones.
6
discovery+ | Stream TV ShowsAhigher tier
Free + IAP · ★ 4.9 · 918,561 ratings · score 87
Streaming app with original series and shows from brands including HGTV, Food Network, TLC and Discovery Channel.
7
Gaia: Streaming ConsciousnessBhigher tier
Free + IAP · ★ 4.8 · 140,911 ratings · score 72
Streaming app with films, original shows, yoga, meditation and documentaries on personal growth, metaphysics and…

What is the best alternative to Thirteen Explore on iPhone?: CuriosityStream, S tier, #1 in documentary streaming.
Is there a free alternative to Thirteen Explore?: Yes: CuriosityStream (S tier, #1) is free to download, with in-app purchases.
Does anything rank above Thirteen Explore?: Yes. 7 apps rank above it in documentary streaming: CuriosityStream (#1), MagellanTV Documentaries (#2), Kanopy (#3) and more.